Electric unit.



F. M. FURBER.

ELECTRIC UNIT. APPLICATION men MAR. 27, 1917.

1,234, 1 49. Patented July 24, 1917.

S85 the sharp curvature there causes the wire to this disorganizingtend- UNITED STATES PATENT FREDERICK I. FUBBEB. OF REVERE,MASSACHUSETTS, ASSIGNOR TO UNITED SHOE IAGHINEBY COMPANY, OF PATEBSON,NEW JERSEY, A CORPORATION OF NEW JERSEY.

ELECTRIC UNIT.

To all whom it may concern:

Be it known that I, FREDERICK M.' F UR- man, a citizen of the UnitedStates, residing at Revere, in the county of Suffolk and State ofMassachusetts, have invented certain Improvements in Electric Units, ofwhich the following description, in connection with the accompanyingdrawings, is a ecification, like reference characters on t e drawingsindicating like parts in the several figures.

This invention relates to electric heating units of general utilitly.

Heretofore when e ectric units have been used in situations where'theyare subjected to severe shocks or vibrations it has been reason of thebreaking of the resistance wire found that they deteriorate rapidly andthat the repeated stress to which they are thus subjected leads to theirdestruction in a short time.

Great difliculty has been experienced by where itsends are fastened:This wire is in a manner involvin themselves,

to produce disorganization of molecular ,ar

' to yield rapidly often very small, and in units asheretofore.

constructed, has been fastened at its ends some form of more or lesssharp bend. his, of course, puts one side of the wire in tension and theother side under compression, and when such units are used in situationswhere they are subject to rapidly recurring shocks, which, in as is wellknown, tend strongly rangement, the non-homogeneity of intermolecularstress at the bend produced by ency, with the result that it soonbreaks.

Another cause of damage at this point is corrosion at thecjunction oftheresistance wire and the terminal member to which it is fastened. Thecause of this corrosion is somewhat obscure, but may be connected withthermo-electric effects due to the heatin of the junction of twodissimilar metals. Ttesistance wire is selected solely with'regard toits qualities as a durable resistance,

and its composition is therefore determined largely without regard toany possible relation it may have to other parts of the unit. Terminalmembers have been heretofore selected with re ard to mechanicalconsiderations alone. have found that by properly selecting the materialof which the terminal member is made, with regard to Specification ofLetters Patent. Patented July 24, 1917,

Application filed larch 27, 1917. Serial K0. 157,782.

the material of which the resistance wire is constructed, (or viceversa), the corrosion of the parts at the junction of the wire andterminal members, and consequently the destruction of the unit, can beavoided.

The unit shown in the accompanying drawings is designed particularly foruse in shoe machiner where the space for it is extremely limite andwhere it is subjected to swiftly recurring jars and shocks. Thelimitation as to space enforces the use of very small wire, less than0.01 inch in diameter, and the violent treatment which theunit'undergoes makes imperative the preservation of the wire from anycorrosion, since a very small degree of deterioration will destroy it.

I have found that corrosion at the junction of the wire and terminalblock can be obviated by avoiding too great a chemical dissimilarity inthe elements composing the joint. I conceive that the presence in theseelements of elements belonging)to the same belonging to the same chemicagroup in its composition. In the unit described this group is theiron'group, and the specific elements are iron and nickel.

This and other features of the invention will be understood from thefollowing description of a preferred embodiment of the invention,selected for purposes of illustration and shown in the accompanyingdrawings, in which; a

Figure 1 is a section of the head of a burnishing machine showing theunit in elevation; Fig. 2 is an enlarged elevation of the unit partly insection on the line 2--2 of Fig. 1; and

Figs. 3, 4 and 5 are details showing the manner of fastening the ends ofthe resistance wire.

The shaft 10 is oscillated'rapidly in suitable bearings not shown. Itcarries the head 11 upon which is-mounted the tool carrier 12, whichsupports the burnishing tools 13. The tool carrier 12 has a bore 14 inwhich is mounted the unit and which has a mica floor 14. Slots 15 in thewalls of the upper end of the bore 14 permit the egress of the leadwires.

The unit is built up on a nickel steel rod 16, having a head 17 at oneend. To this head is brazed one of the flexible lead wires 18, whichcarries a lava bead 19, a number of glass beads 20 and the terminal 21.The lava head 19 rests in the slot 15 and resists, better than a glassbead, the intense heat at this point.

Next to the head .17 on the rod 16, is mounted a mica washer 22, whichis of larger diameter than the head 17 and just fits the bore 14. Nextto the mica washer 22 24 and is helically threaded throughout its Ilength. Next to the core is mounted in electrical contact with the rod16, a nickel steel terminal 26 of the same diameter as the core, andnext to the terminal 26 is mounted another mica washer 27, indenticalwith the washer 22. Below this is mounted a steel washer 28 upon whichthe rod 16 is upset at 29.

i The resistance wire 30 is wound in the helical thread,'and fastened toits terminal elements 24, 26 in the manner shown in' Figs. 3, 4 and 5. Aslot 31 is cut in each]. of the elements 24, 26, the ends of the wirelf? 30 are placed in h Sl an a h of t i jciently elastic to take up therelative expansion, necessarily minute, as shown, of the lips 32 is thenupset overthe wire by a punchstroke, clamping itfirmly in position.

Of the numerous kinds of resistancelwire obtainable on the market, Ihave found the Driver-Harris Wire Companys nichrome wire the mostsatisfactory. This wirecon- :tains or more of nickel andasma'llerpercentage of chromium. ifThoughtheL- performance and durability-of thiswirefasiare sistance were found adequate, and theterininalfastenmg'means prevented mechanical destruction at the joint,considerable difficulty was at first experienced with corrosion at thispoint, the terminal rings 24 and 26 being of copper in the first unitsmade. I found that by replacing the copper with a material having acloser relation to the wire 1n regard to chemical composition, thecorrosion difliculty could be avoided. A convenient material for thispurpose was found to be nickel steel, no appreciable corrosion appearing1n the units in which it was used for terminals. I regard this freedomfromcorrosion as due to the presence of .chemi-f amount of materialbelonging to the same chemical members.

The current flows through the wire 18, head 17, rod 16, terminal 26,wire 30, rmg 24, to the wire 25. The washers 22, 27 project beyond theouter cylindrical portions of the unit, and insulate it from the wall ofthe bore 14. The floor 14' insulates the end of the rod 16. Thenecessity of a cover or case for the unit is thereby avoided, and theheat is more easily and directly conveyed to the tools.

The lava used in the core 25 has a mean thermal coefiicient of expansionbetween F. and 935 F., (just visible red) of 0000,0070 per 1 F., whichis substantially that of steel. The nickel steel rod 16 used in the unitdescribed has a mean thermal coelficient of expansion between the samelimits of 0000,00? 6 per 1 F. The relative coefficient of expansionbetween these limits per 1 F., is, therefore, 0000,0006. The

group in both of the joint forming unit itself is about 21: inches long.The I ,ed on the rod 16, and will safely take stresses Ifdue to theheading up of the rod 16, which might crush a more unyielding structure.

At the same time the washers are suffinickel steel rod 16 and the lavacore 25', when heated in use. The materialsof the unit supported on therod 16 are thus bonded togetherin a compact mass, always under asubstantial compression. I have found that the'layagcore is veryresistant to shocks and that when'it' does break, it breaks crosswise.and-.not lengthwise. The longitudinal compression exerted by the rod 16upon the core'efiectively precludes danger of breakage of this sort.

The-means adopted for fastening theends I of the resistance wire avoidsthe heretofore experlenced breakage of the wire at these points. Theslot31 is substantially in the is wound on the unit, and the wire enters itwithout substantial bending; The upsetting prolongation of the helix inwhich the wire of the sides of the slot on'the wire applies a pressureto the wire which is substantiallyincreases from zero to a maximumlongiuniform circumferentially and progressively,

'tudinally, from the ends of the slot to-"its middle so that sharpvariations in molecular stress are avoided. It will be seen that in theunit shown, all the resistance wire is open to inspection andmanipulation and that aburnedput wire can be readily replaced by theoperator, by merely spreading the slots 31 and upsetting them again.

I do not claim broadly the use of nickel in a'terminal member herein, asI have claimed it in my co-pending application Serial No. 36,721, filedJune 28, 1915.

Having described the invention, what I claim as new and desire to secureby Letters Patent of the United States is:

1. An electric unit having resistance wire, and a terminal member towhich it is fastened, the wire and member each containing a substantialquantity ofmaterial belonging to the same chemical group.

2. An electric unit having resistance wire, and a terminal member towhich it is fastened, the wire and member each containing a substantialquantity of material belonging to the iron group.

3. An electric unit having resistance wire and a terminal member towhich it is fastened, the wire and member containing substantial amountsrespectively, of different materials belonging to the same chemicalgroup.

4. An electric unit having resistance wire with nickel in itscomposition, and a terminal member for said wire having nickel in itscomposition.

5. An electric unit having resistance wire with nickel and chromium inits composition, and a terminal member of nickel steel for said wire.

In testimony whereof I have signed my name to this specification.

FREDERICK M. FURBER.

copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Iatents,

Washington, I). G.

